It happened after Fuquay-Varina officers were called to the Abby Rd. Bar at 711 N. Main St. for a report of a suspicious vehicle.
The officer responding saw the vehicle, running, in a parked position a few inches from the building.
Ryan Michael Bentkowski, 24, was passed out in the driver's seat while the vehicle was running, police said.
Bentkowski was asked to get out of the vehicle and show the officer his driver's license.
During Bentkowski's arrest, Fuquay-Varina police said he showed a sheriff's office badge as a form of identification. According to police, he said he worked with the sheriff's office.
The Wake County Sheriff's Office said he also had a jacket with patches, ball cap, and a sealed gas-mask cartridge.
When Fuquay-Varina police contacted the sheriff's office, they were told he was not a current employee.
The Wake County Sheriff's Office said Bentkowski was placed on administrative leave Sept. 16 after he was served with a domestic violence protective order. He was fired from the sheriff's office on Sept. 30.
The Sheriff's Office said deputies were sent to his home Sept. 30 to retrieve his service weapon, vest, and patrol vehicle. Bentkowski told the deputies he couldn't find any other WCSO-issued equipment.
The items that Fuquay-Varina officers found with Bentkowski matched the missing equipment, the sheriff's office said.
Bentkowski has been charged with driving while impaired, carrying a concealed gun, and impersonating a law enforcement officer. He may face additional charges, the sheriff's office said.